Mr. Riley is a wacky gent. If you're into a trippy band there is a good chance Terry had a hand in the production. Steve Reich, Philip Glass, John Adams, The Who, The Soft Machine, Curved Air, Tangerine Dream...the list goes on. This recommendation is dedicated to James Murphy of LCD Soundsystem who believes no "taste engine" would ever suggest Terry Riley.
@gleitz : don't blame James, he just hasn't used Hunch [yet] ;) If you like Riley, I'd also recommend the music of La Monte Young and the Dream Syndicate, a collaborative ensemble that articulated the Big Bang of "minimalism".